Development and validation of an instrument to determine patient knowledge: the oral anticoagulation knowledge test

Studies examining the relationship between patient knowledge regarding warfarin therapy and its safe and effective use are limited by the lack of validated knowledge assessment tools.

To develop and validate an instrument to assess patient knowledge regarding oral anticoagulation therapy.

Four nationally recognized anticoagulation experts participated in the instrument development process to ensure content validity. The Oral Anticoagulation Knowledge (OAK) test was administered to subjects on warfarin and a group of age-matched subjects not on warfarin to assess construct validity. A subgroup of warfarin subjects were retested approximately 2-3 months after initial testing to assess test-retest reliability. Internal consistency reliability was assessed by calculating a Kuder-Richardson 20 value. Item analysis was used to assess performance of individual questions.

An initial 23 item instrument was pilot tested for readability and comprehension. The OAK test was administered to 74 subjects taking warfarin and 27 age-matched subjects not on warfarin. Thirty-two subjects on warfarin repeated the OAK test an average of 75 days following initial administration. Subjects taking warfarin scored significantly higher than those not on warfarin (72% vs 52%, respectively; p < 0.001), supporting the construct validity of the instrument. Test-retest reliability was acceptable, with a Pearson's correlation coefficient of 0.81. Internal consistency reliability was confirmed by a calculated Kuder-Richardson 20 value of 0.76.

The OAK test is a brief, valid, and reliable knowledge assessment instrument that may be a useful tool for research and clinical practice to augment patient education programs.